A unified description of initial and final state interactions in heavy ion collisions

We have investigated the gauge field of a fast moving projectile passing through a dense medium. We provide a simple and unified derivation, in light cone gauge, of the gluon production cross-section in proton-nucleus (initial state interactions), and the radiative gluon spectrum of a hard parton produced in a nucleus-nucleus collision (final state interactions). Finally, we discuss the validity of the eikonal approximation in proton-nucleus collisions at RHIC energies.